(1) Field of the Invention
The present invention pertains to a bearing assembly that is equally well-suited for use in self-aligning and rigid shaft supporting applications. More particularly, the bearing assembly of the invention permits one bearing bushing to be employed in both applications that permit self-aligning pivoting movement of the support for a rotating shaft and applications that rigidly support a rotating shaft, thereby eliminating the need to inventory two different types of bearings for these two different applications.
(2) Description of the Related Art
Self-aligning bearing assemblies are often used in environments where the bearing assembly provides support from a structure to a rotating shaft while permitting a limited degree of shaft pivoting movement relative to the supporting structure. A typical application of this type is found on the output shaft of an electric motor, although self-aligning bearing assemblies are employed in various other applications. This illustrative environment of the prior art self-aligning bearing assembly is shown in drawing FIGS. 1-3.
The typical prior art self-aligning bearing assembly is comprised of a bearing seat 10, a bearing bushing 12, a retaining ring 14, and a sealing cap 16.
In the application shown in FIGS. 1-3, the bearing seat 10 is formed as part of an end shield 18 of an electric motor housing. The bearing seat 10 is cast integrally with the housing end shield 18. Aluminum is often employed in casting the bearing seat and the end shield. The bearing seat has a shaft opening 20 through its center. When the end shield 18 is assembled to an electric motor (not shown) the rotor shaft of the motor will pass through the shaft opening 20. A bearing land surface 22 supports the bearing bushing 12 in sliding engagement extends around the shaft opening 20. In some bearing seats the land surface extends as a single continuous surface around the shaft opening, and in other bearing seats the land surface is actually formed as several separate surfaces that are spacially arranged around the shaft opening. In the illustrative prior art shown in FIGS. 1-3, the bearing land surface 22 is shown as three separate surface sections spacially arranged around the shaft opening 20. In cross-section, the land surfaces 22 have a concave configuration. Together the land surfaces 22 define a cup or socket shape with the shaft opening 20 at the bottom, center of the socket shape.
Referring to FIG. 2, the prior art bearing bushing 12 has a semi-spherical forward end 24 and a cylindrical rearward end 26. A shaft bore 28 extends axially through the center of the bushing. The interior diameter of the shaft bore 28 is sized to securely mount the motor shaft for rotation in the bore. The semi-spherical forward end 24 of the bushing is defined by the spherical shape of the bushings bearing surface 30 that mates in sliding engagement with the land surfaces 22 of the bearing seat. The shape of the bearing surface 30 is complimentary to the curvature of the bearing seat land surfaces 22. This enables the bearing bushing 12 to pivot to a limited extent on the bearing land surfaces. The bearing bushing 12 is often constructed of powdered metal iron graphite that is a softer material than the aluminum employed in constructing the bearing seat 10. The powdered metal of the bearing bushing is also porous which enables the bearing surface 30 to retain lubricant which enhances its ability to pivot on the bearing seat land surfaces 22.
The method of assembling the prior art self-aligning bearing assembly is shown in FIG. 1. The motor end shield 18 is shown placed face down with the interior surface 32, or that surface that would face the stator and rotor of the electric motor, facing upwardly. The bearing seat 10 is shown at the center of the end shield 18. The bearing bushing 12 is placed in the bearing seat 10 with the bearing surface 30 of the bushing resting on the land surfaces 22 of the bearing seat. A tooling pilot shaft 34 is inserted through the shaft bore 28 of the bushing. The retaining ring 14 functions somewhat like a Belleville spring and is placed over the shaft and press-fit into a cylindrical collar 38 of the bearing seat that extends upwardly from the land surfaces 22. Projecting tabs 40 of the retainer engage against the interior surface of the cylindrical collar 38 and hold the retaining ring in its position pressed downwardly into the cylindrical collar. A center ring 42 of the retainer passes around the cylindrical rearward end 26 of the bearing bushing and engages against an annular shoulder 44 of the bearing bushing that separates the cylindrical rearward end 26 from the semi-spherical forward end 24. When inserted completely into the cylindrical collar 38, the center ring 42 of the retaining ring 36 exerts a biasing force against the annular shoulder 44 of the bearing bushing that forces the bearing surface 30 of the bushing into engagement with the land surfaces 22 of the bearing seat. This biasing force also produces the correcting or centering force on the bearing bushing 12 that urges the bearing bushing 12 to return to a position where a center axis passing through the bearing bushing shaft bore 28 is aligned coaxially with a center axis passing through the bearing seat shaft opening 20. In completing the construction of the prior art self-aligning bearing assembly, a lubricant may be applied within the cylindrical collar 38 of the bearing seat 10 and then the sealing cap 16 is press-fit into the cylindrical collar 38 to retain the lubricant and complete the assembly of the self-aligning bearing assembly.
A primary benefit provided by the self-aligning bearing assembly is that the motor end shield 18 does not have to be perfectly aligned with the center axis of the electric motor rotor and stator when the end shield is assembled to the motor, i.e., the center axis (not shown) of the end shield bearing seat shaft opening 20 does not have to be perfectly aligned with the center axes of the electric motor rotor and the electric motor stator. If these axes are not perfectly aligned when the end shield 18 is assembled to the electric motor, the bearing bushing 12 will pivot slightly on the bearing seat land surfaces 22 to compensate for the misalignment and thereby support the motor shaft for rotation in the end shield 18 without having the end shield perfectly oriented relative to the shaft.
In the construction of electric motors, there are applications where the motor end shield must be properly positioned relative to the shaft. In these applications, the end shield itself is used to orient the motor shaft relative to the environment in which the motor is used. For example, where the electric motor is used to power a transmission such as a gearing transmission, the motor end shield would typically be connected directly to the supporting structure, i.e., the casing of the gearing transmission. If the motor shaft was improperly oriented relative to the motor end shield, for example if the shaft center axis was not perfectly aligned with the center axis of the end shield shaft opening, then the shaft would not be perfectly aligned with the center axes of the gears employed in the gearing transmission attached to the motor end shield. This would result in gears of the transmission not properly meshing with each other and often produced accelerated and uneven wearing of the gear teeth. Similar problems would also occur in other environments. For example, if the motor were powering a belt and pulley transmission, the center axis of the drive pulley mounted on the motor shaft would not be aligned parallel with the driven pulley of the transmission. This would also result in accelerated wear of the belt connected between the drive and driven pulleys. Also, if the motor were used to power a pump, the misalignment of the motor shaft and the pump shaft could cause pump seals to wear and leak. Therefore, in those applications where it was required that the motor shaft center axis be aligned with the center axis of the end shield shaft opening, a fixed bearing assembly was needed which would hold securely the shaft relative to the motor end shield and not permit any misalignment or pivoting movement of the motor shaft.
The two different environments described above have required two different bearing assemblies, i.e., one bearing assembly that would permit self-aligning movement of the motor shaft relative to the supporting structure or end shield of the bearing seat, and a second bearing assembly that would hold the motor shaft securely relative to the supporting structure or the bearing seat of the motor end shield. This required manufacturers of electric motors to inventory two different types of bearing assemblies for their motors which resulted in incurring additional costs for inventorying these two different types of bearing assemblies.